GENETICS

Genetics Video Clips Learn about Heredity http://www.neok12.com/video/Genetics/zX537c467973705973775d59.htm What are genes? http://www.neok12.com/video/Genetics/zX57774078797d7564675a0a.htm Where do genes come from? http://www.neok12.com/video/Genetics/zX5e724c6f0042150202670a.htm

Terms Gene: a segment of DNA with coded information for a particular trait or characteristic. Because animals are diploid (have two sets of chromosomes) there are 2 genes for each trait…one inherited from each parent.

Terms Allele: Actual DNA “letters” found in the chromosome One allele is inherited from each parent for each genetic trait

terms Dominant allele: alleles which hide or mask the information carried by recessive alleles. Dominant allele = capital letters Dominant alleles takes over when there are 2 dominant alleles or a dominant and recessive allele are present. Examples: RR or Rr

terms Recessive allele: alleles that only show up as a trait in someone when NOT paired with a dominant allele Recessive alleles = lower case letters Recessive traits only show up in people when there are 2 copies present. Example: rr

Genotype: the 2 alleles inherited for each genetic trait the actual genetic info (represented by letters). Like RR, hh, Rr, etc. Homozygous: 2 copies of the same allele for a trait. Ex: RR or rr Heterozygous: 2 different alleles for a trait Ex: Rr

Terms con’t Phenotype: physical appearance of the trait which can be seen. Examples: if a person has brown hair or blond hair or if they have a disease or not

What is a phenotype? http://www.neok12.com/video/Genetics/zX5870617f4648547e590445.htm

Let’s Review Homozygous or heterozygous? Homozygous

Let’s Review Homozygous or heterozygous? heterozygous

Let’s Review What is this flower’s genotype? Ff (heterozygous)

Let’s Review What is this flower’s phenotype? purple

Let’s Review Is this flower homozygous or heterozygous? heterozygous

Let’s Review What is this flower’s phenotype?. white

Let’s Review What is this flower’s genotype? ff

Homozygous versus Heterozygous Practice Genotype versus Phenotype Practice

Cracking The Code Of Heredity

The study of heredity, how traits are passed from parent to offspring Genetics The study of heredity, how traits are passed from parent to offspring or x = or

Mendel & Heredity Heredity was a mystery for a long time It was thought that parents’ traits blended in the next generation…like red and white blend to make pink But in reality traits are NOT always inherited this way

Gregor Mendel Austrian monk “The Father of Genetics” The first person to start unraveling the mystery of heredity in the 1800s

Mendel’s experiments Modern genetics began with Gregor Mendel’s experiments with pea plants Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation

Mendel’s law of segregation Parents have two alleles for every trait, but only give one allele to a gamete (sex cell) In the offspring, one allele comes from each parent

GENETIC CROSSES (ONE TRAIT)

The inheritance of many human traits follows Mendel’s principles and the rules of probability

Punnett squares Punnett square: a box like diagram used to predict all possible genotypes that result from a cross Punnett Square Quick Tips: Find out which alleles are dominant or recessive Write each parent’s genotype Fill in Mom’s genotype on the top of the punnett square and the Dad’s along the side of the punnett square Complete boxes to see all the possible genetic cross outcomes or kids’ genotypes

LAYOUT OF PUNNETT SQUARES Kids’ Genotypes Punnett square basics clip: http://youtu.be/prkHKjfUmMs Dad's genotypes Mom's Genotypes

PUNNETT SQUARES: Monohybrid crosses-- A cross between organisms that involves only ONE pair of traits Example 1: Having freckles is dominant trait. What is the chance that a child will have freckles if DAD is homozygous for freckles and MOM does not have freckles? 4/4 f f Gene Notation Symbols F = freckles f = no freckles Ff Ff F Parent Genotypes: MOM: ff DAD: FF F Ff Ff

Monohybrid CROSSES cont… Example 2: Widow’s peak is a dominant trait. What is the chance that a child will have a straight hairline if DAD is heterozygous for widow’s peak and MOM has a straight hairline? 2/4 p p Gene Notation Symbols P = widow’s peak p = straight hairline Pp Pp P Parent Genotypes: MOM: pp DAD: Pp p pp pp

Law of Independent Assortment Allele pairs separate independently of each other during gamete formation (meiosis) Which means…. Different traits appear to be inherited separately

Monohybrid Cross Practice 1—do together as a class Monohybrid Cross Practice 2—do on your own

Genetics Drama #1 Monohybrid How Could Our Baby Be Albino?? Monohybrid quiz tomorrow!!

INCOMPLETE DOMINANCE, CODOMINANCE AND SEX-LINKED TRAITS

VARIATIONS ON MENDEL’S PRINCIPLES The inheritance of some traits is more complex than Mendel’s principles can explain

Incomplete dominance Sometimes the 2 alleles for a trait BLEND together creating an intermediate phenotype = incomplete dominance NEITHER ALLELE IS DOMINANT Red RR White rr R r Pink Rr 1/2 R 1/2 r 1/2 R 1/2 R Eggs Sperm Red RR 1/2 r 1/2 r Pink Rr Pink rR White rr F2 GENERATION Figure 9.12A

Incomplete dominance cont… Heterozygotes (Rr) show an intermediate phenotype RR = red flowers rr = white flowers Rr = PINK flowers

Codominance Codominance is when both traits are fully and separately expressed Both alleles show up Example: white and red flower crossed makes a flower that shows both red and white on its petals

Looking at blood types can show some examples of codominance… Human A, B, AB, & O blood types are determined by 3 alleles in the human gene pool: A, B, or O The alleles for A and B blood types are both dominant (codominant) The O allele is recessive = o This means that there are two dominant alleles and one recessive allele, but if the two dominant alleles are together, then they are both expressed (A + B = AB blood type)

Blood types Phenotype Genotype Type A Blood AA or Ao Type B Blood BB or Bo Type AB Blood AB Type O Blood oo See blood type punnett square examples at: http://www.cccoe.net/genetics/blood.html

Type A = AA or Ao Type B = BB or Bo Type O = oo Codominance cont… Example 1: List all the possible blood genotypes and phenotypes and their ratios for children conceived from a male heterozygous for type A blood (Ao) with a woman with homozygous type B blood (BB). Type A = AA or Ao Type B = BB or Bo Type O = oo Parents’ genotypes MOM = BB DAD = Ao

Codominance practice

Genetics Drama #2 Codominance Were the Babies Switched??

SEX-LINKED TRAITS XX A human female = A human male = Chromosomes determine sex (gender) in many species XX A human female = A human male = A baby’s gender depends on whether Dad’s sperm delivers a X or Y chromosome So, should Henry the 8th have executed all of his wives for not giving him sons? XY

Genes on sex chromosomes Y chromosome = Sex-regulation gene master gene for maleness & male hormones X chromosome = other traits beyond sex determination Duchenne muscular dystrophy affects one in 3,500 males born in the United States. Affected individuals rarely live past their early 20s. This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin. The disease is characterized by a progressive weakening of the muscles and loss of coordination.

Sex-linked traits have genes on the X chromosome Human X chromosome Sex-linked traits have genes on the X chromosome more than 60 diseases are traced to genes on X chromosome, including: Hemophilia Duchenne muscular dystrophy color-blindness

Sex-linked traits All genes that are carried on the X chromosome are considered to be sex-linked In many organisms, the X chromosome carries many genes unrelated to gender Fruit fly eye color is a sex-linked characteristic

Connection: Sex-linked disorders affect mostly males Most sex-linked human disorders are due to recessive alleles Examples: hemophilia, red-green color blindness A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the recessive X allele from both parents to be affected

Color Blindness Test A B C D

E F

Sex-linked traits cont… Example 1: Color-blindness is a sex-linked trait. Jim is not colorblind and neither is his wife, Mary. However, because Mary’s dad WAS colorblind, she is heterozygous for red-green colorblindness. What are the chances that a daughter will be colorblind? What about a son? What are the chances that a daughter will be a carrier? Gene Notation Symbols XBXB = female non-carrier XBXb = female carrier XbXb = female colorblind XBY = male normal XbY = male colorblind Parents’ genotypes MOM = XBXb DAD = XBY

Sex-linked traits, example 1 cont… 1st generation phenotypes: ½ females will be normal, ½ females will be carriers, ½ males will be normal, ½ males will be colorblind The chance of having a colorblind child is ¼. XB Xb XB XBXB XBXb XBY XbY Y

I Don’t’ Want To Have Colorblind Daughters!! Genetics Drama #3 I Don’t’ Want To Have Colorblind Daughters!! Later… Punnett Square practice on all types of crosses